Note:
If the option Scan for performance issues is not in your Scan menu, then Avast Antivirus 2015 has determined that your system is incompatible with running Avast GrimeFighter for some reason. More...

Avast GrimeFighter may take anywhere from 30 minutes up to four hours to scan your computer. During the scan you can browse the Internet, but keep in mind that you won't be able to access any of your Windows files or applications.

If you need to return to Windows during a scan, you can exit Avast GrimeFighter by clicking the cross in the top right corner of the screen, and select Reboot.

When the scan is complete, you have the option to review changes before performing the cleanup:

If you want to accept all recommended changes to your computer, click Clean My System.

Figure V

Otherwise, to view the recommended changes before performing the final system cleanup, click Review and Edit Changes, and set which action you want to apply for each item, one by one. When you are finished reviewing click Apply Changes,

Figure VI

...and then select Clean My System.

After Avast GrimeFighter has finished cleaning your system, a summary of the changes appears. Points are a rough numerical representation of work done in each area.

Figure VII

Click Return to Windows to restart your computer in Windows.

If there is any problem you have 7 days to undo the changes. For details please visit the following article: